The trait of double-flowered or multi-flowered petals is one of the important factors for ornamentalness of garden plants. Introduction of morphological traits into flowers of garden plants, such as producing multi-flowers via genetic engineering techniques may produce a great diversity of varieties in shorter periods of time than the conventional crossbreeding techniques.
MADS-box genes are a family of genes consisting of 30 or more genes that encode transcription factors having a conserved region called MADS-box. Many of these genes have been shown to regulate morphogenesis and organogenesis of plants by way of transcriptional regulation. Many of the genes of the three classes of homeotic genes that are responsible for development of floral organs (the ABC model) are MADS-box genes and have been studied in detail (Sakai, H. (2000). “Molecular genetics of floral morphogenesis,” in: “Molecular Mechanisms for Determination of Plant Morphology,” 150–163 (Shujunsha Inc.); Goto, K. (1994). “The ABCs of Flower Development: Genetic and Molecular Analyses of Floral Homeotic Genes,” in: Molecular Mechanisms for Determination of Plant Morphology, 52–61 (Shujunsha. Inc.); and Weigel, D., and Meyerowitz, E. M. (1994). Cell 78, 203–209).
One of the MADS-box transcription factors isolated from Petunia, pMADS3 (MADS3 derived from Petunia), is a homeotic gene involved in specificity of floral organs. Its structure and expression pattern suggest that pMADS3 belongs to Class C of the floral ABC model. It was revealed that homeotic mutations, such as formation of antheroid structure (staminody) at the tip of petals and, occasionally, carpelloid structure at the tip of sepals, occur in transgenic petunia plants that ectopically express the pMADS3 gene. Such mutations also suggest that MADS3 is a member of the Class C genes (Tsuchimoto, S. et al. (1993) Plant Cell 5, 843–853; Takatsuji, H. (1994). “Transcription Factors Controlling Floral Organ Development,” in: Molecular Mechanisms for Determination of Plant Morphology, 96–106 (Shujunsha Inc.)). The cDNA sequence of pMADS3 has been reported in Tsuchimoto, S. et al. (1993). Plant Cell 5, 843–853.
As described above, many reports on MADS-box transcription factors and their functions in floral organogenesis in plants are available. However, so far no one has reported success in producing highly ornamental plants, such as multi-flowered plants, using a MADS-box transcription factor as the target.